A wide variety of mechanical heart valve prostheses have been developed to operate hemodynamically, in conjunction with the pumping action of the heart, which are designed to take the place of defective or diseased natural valves. These valves typically have valve bodies which accommodate valve members either in the form of a single occluder or in the form of multiple occluders or leaflets, wherein these valve members generally pivot along eccentric axes to open and close a central blood flow passageway through the valve body. Alternatively, some mechanical valves utilize valve members that both pivot and translate to open and close a central blood flow passageway.
In its open position, a prosthetic heart valve desirably provides a central blood flow passageway which is large and which has good flow characteristics so that blood flows freely therethrough without adverse boundary layer separation and with a minimum of drag. A heart valve mounted in the aortic position should be very responsive to blood flow so as to open quickly during the pumping stroke of the heart and to close quickly when the associated chamber of the heart relaxes so as to prevent substantial regurgitation of the blood. The opening and closing of the valve should be sufficiently soft so that the patient is not disturbed by the sounds produced and so that the impacts on the valve body are minimal. The heart valve must be made of materials that are biocompatible and thromboresistant, and in this regard, it is important that all surfaces be well washed by blood to prevent regions of stagnation which might lead to eventual clotting. Furthermore, the action of the valve should be such that it does not cause hemolysis (damaging of blood cells), and of course, the heart valve should be constructed to withstand countless openings and closures without the valve members jamming or escaping.
Prior art multi-leaflet heart valves have offered a variety of designs and configurations intended to address the some of the aforementioned problems. For example, U.S. Pat. No. 4,272,854 (Jun. 16, 1981) shows an early version of a bileaflet heart valve having an ear extending from each lateral side of each leaflet, which ear pivots in a recess, guided in part by a knob traveling in a longitudinal slot that is cut more deeply into the sidewall of the valve body.
U.S. Pat. No. 4,363,142 (Dec. 14, 1982) discloses a bileaflet heart valve wherein the leaflets have laterally extending ears in the form of generally oval or spherical projections that are received in recesses of complementary design.
U.S. Pat. No. 4,373,216 (Feb. 15, 1983) discloses a bileaflet heart valve wherein protrusions, extending generally radially inward from a pair of flat sidewall sections of the valve body, guide valve members which have slots in their lateral edges which fit about such protrusions. U.S. Pat. No. 4,451,937, (Jun. 5, 1984) shows a generally similar bileaflet heart valve where the pivot arrangement is formed with a reversal of parts wherein the leaflets have laterally protruding ears which are received within slots in the valve body sidewall that guide the opening and closing movements.
U.S. Pat. No. 4,308,624 (Jan. 5, 1982) discloses heart valves of both the single occluder and bileaflet type having curved valve members which both rotate and translate in moving between the open and closed positions, being guided by laterally extending ears that travel in slots. Later versions of this valve are disclosed in U.S. Pat. No. 4,357,715 wherein an elongated depression within each slot in the valve sidewall controls lateral movement within the slot, and also in U.S. Pat. No. 4,443,894 (Apr. 24, 1984) wherein the slots are of kidney bean shape.
U.S. Pat. No. 4,808,180 (Feb. 28, 1989) discloses a bileaflet valve wherein the leaflets each have a semi-conical shape and thus inherently provide significant resistance to blood flow through the valve in the open position. The leaflets are guided by generally C-shaped rails that protrude from the valve body sidewall and are received in recesses of complementary shape in the lateral edges of the semi-conical leaflets.
U.S. Pat. No. 5,207,707 (Jan. 16, 1992) discloses a trileaflet heart valve wherein the leaflets translate between open and closed positions guided by ears 74 which travel along curved grooves 40 situated within walls of a pivot structure 26. U.S. Pat. Nos. 4,820,299 and 5,123,918 also disclose trileaflet prosthetic heart valves, with the latter illustrating a construction wherein specially configured arcuate members protrude from the interior valve body surface and guide such leaflets in moving between the open and closed positions.
Commercially developed heart valves, such as the St. Jude Medical valve, have generally employed valve members oriented at a significant angle to the valve centerline in the open position, so that the backflow of blood preferentially impinges strongly upon the outflow surfaces of each valve member in order to initially impart a strong pivotal force component in the direction of closing movement. It is now felt to be particularly important that a mechanical heart valve prosthesis should provide a passageway through which blood can freely flow in the open position with a minimum of drag. To accomplish this desired objective, it is now believed that the valve members should be able to follow the flow and, when required, assume orientations which are generally parallel to the longitudinal axis of the passageway.
In summary, trileaflet heart valves should have such improved flow characteristics in the open position, should be reliable and responsive in leaflet movement and should be designed to avoid the likelihood of clotting. Trileaflet heart valves which meet these criteria continue to be sought.